The polyphenylene oxides and methods for their preparation are known in the art and are described in numerous publications including Hay U.S. Pat. Nos. 3,306,874 and 3,306,875. Manganese based catalysts for the oxidative coupling of phenolic monomers in the formulation of polyphenylene oxides are disclosed in Mc Nelis, U.S. Pat. No. 3,220,979; Nakashio, U.S. Pat. No. 3,573,257 and Nakashio, U.S. Pat. No. 3,787,361. The use of complexed manganese catalysts is disclosed in U.S. Pat. Nos. 3,956,242; 3,965,069 3,972,851; copending applications Ser. No. 753,509; Ser. No. 753,501; Ser. No. 753,506 and Ser. No. 753,507, all of which are hereby incorporated by reference.
The processes which employ homogenous complexed manganese catalysts have been carried out by combining all of the complexed manganese catalysts with the reaction mixture or where a portion of the monomer is added after initiation of the polymerization reaction. The term homogenous is used to describe a completely soluble complexed manganese catalyst which is soluble in an appropriate solvent such as methanol or in the monomer, e.g. 2,6-xylenol. These processes have worked quite well but it has been desirable to reduce catalyst usage, to control reaction rates, to improve performance at high solid levels and increase tolerance to higher water levels during polymerization. It has now been found that the use of a programmed addition cycle which comprises adding the complexed manganese catalyst in increments during the polymerization cycle will reduce by up to 50% the amount of catalyst that is required to oxidatively couple a phenolic monomer. Moreover, the programmed addition of the complexed manganese catalyst results in a more controllable exothermic reaction, improved reaction rates as compared with bulk catalyst addition methods, reduced catalyst losses from hydrolysis from the water formed during the polymerization and improved reaction performance at high levels of solids, i.e. about 24 to 26%. The above results are obtained without adversely affecting the quality of the polyphenylene oxide resin when it is combined with a styrene resin. In addition, the use of a programmed addition of the complexed manganese catalyst may be applied to a continuous polymerization process.
Accordingly, it is a primary object of the present invention to provide an improved process for the preparation of polyphenylene oxide resins which is based on the use of a programmed addition of a complexed manganese catalyst.